package days48;

import java.util.Scanner;

public class six {
    public static void main(String[] args) {
        Scanner scanner=new Scanner(System.in);
        int a=scanner.nextInt();
        int b=scanner.nextInt();
        int [][]arr=new int[a][b];
        int count1=0;
        int count2=0;
        for (int i = 0; i < a; i+=2) {
            count1++;
        }
        for (int i = 0; i < b; i+=2) {
            count2++;
        }
        System.out.println(a*b-count1*count2);
    }
    public static int StrToInt(String str) {
        int sum=0;
        int k=0;
        for (int i = str.length()-1; i >0; i--) {
            if(str.charAt(i)>'9'||str.charAt(i)<'0'){
                return 0;
            }
            sum+=(str.charAt(i)-48)*Math.pow(10,k++);
        }
        if(str.charAt(0)>'9'||str.charAt(0)<='0'){
            return 0;
        }
        if(str.charAt(0)>'0'&&str.charAt(0)<='9'){
            sum+=(str.charAt(0)-48)*Math.pow(10,k);
        }
        if(str.charAt(0)=='-'){
            return sum*(-1);
        }
        if(str.charAt(0)=='+'){
            return sum;
        }
        return 0;
    }
}
